 Seven submarines were lost in the Black Sea, four depth-charged and sunk by Romanian warships ("M-31" by the flotilla leader , "M-58" by the destroyer "Regina Maria", "M-59" by the destroyer "Regele Ferdinand" and "M-118" by the Romanian gunboats "Ghiculescu" and "Stihi")(both "M-58" and "M-59" however are also reported as lost on Romanian laid mines , while "M-31" was also claimed by mines or German boat  )
and three were sunk in minefields laid by the Romanian minelayers , "Dacia" and "Regele Carol I".By 1945, some 111 M-class submarines had been completed, with another 30 XV-series completed between 1945 and 1947.Two submarines of the early series of this class, along with two s, ("S-52" and "S-53") and two s (under lease, "S-121" and "S-123") were sold to the People's Republic of China in June 1954 as the foundation of the People's Liberation Army Navy Submarine Force.